1. Field of the Invention
The present invention relates to a high-frequency input/output feedthrough used for a high-frequency input/output portion of a package for housing a high-frequency semiconductor element for the millimeter wave band or the like, and also relates to a package for housing a high-frequency semiconductor element using the high-frequency input/output feedthrough.
2. Description of the Related Art
A package for housing a high-frequency semiconductor element houses a high-frequency semiconductor element or the like which uses a high-frequency signal in the microwave band, the millimeter wave band or the like, in a hermetically sealed manner. A signal input/output portion of such a package generally employs a structure in which a microstrip line formed on a dielectric substrate and a strip line of a hermetic seal portion are joined together as high-frequency transmission lines, and the high-frequency semiconductor element housed in the package in a hermetically sealed manner is connected to an external circuit via a high-frequency input/output feedthrough thus structured.
As such a high-frequency input/output feedthrough, Japanese Unexamined Patent Publication JP-A 5-183301 (1993), for example, discloses a package input/output portion for super-high frequency band, comprising a line portion forming a hermetic seal portion of a package, an outer line portion for connecting to the outside of the package and an inner line portion for connecting to an internal circuit, the outer and inner line portions being connected to respective ends of the line portion, wherein the length of the line portion forming the hermetic seal portion is selected to be xc2xd n (n is a natural number), namely an integral multiple of xc2xd, of a signal wavelength.
According to this package input/output portion, the length of the line portion of a strip line portion or the like forming the hermetic seal portion is selected to be an integral multiple of xc2xd of the signal wavelength xcex, so that it is possible to prevent a reflection caused by the difference of transmission modes due to the difference of shapes in the outer line portion and the line portion and in the inner line portion and the line portion, and prevent a reflection caused in a case where the characteristic impedance is different because production accuracy is not sufficient and hence the dimension deviates from a design value. Accordingly, the package input/output portion can be produced in a simple fashion to reduce a cost, and can prevent a reflection to improve characteristics in the super-high frequency band.
The conventional high-frequency input/output feedthrough thus configured has been produced in the following manner. Respective line portions are formed by a metallized metal layer made of tungsten, molybdenum or the like on a dielectric substrate made of alumina ceramics or the like, on which an upper dielectric forming a hermetic seal portion is joined, or on which a cap formed by a dielectric material is adhered after a dielectric coating is applied to the line portion of the hermetic seal portion. After that, a plating layer of, for example, nickel and gold is adhered to the surface of the metallized metal layer of the exposed line portion so that a bonding wire or bonding ribbon made of gold is preferably joined thereon.
Further, there are provided packages for housing a high-frequency semiconductor element equipped with the thus configured high-frequency input/output feedthrough in various configuration types such as a so-called metal wall type that a metal substrate and a metal frame forming a case wall are cut away to form an attaching portion for fitting the high-frequency input/output feedthrough thereinto; a so-called ceramic wall type that in a dielectric substrate and a dielectric frame forming a case wall is formed an attaching portion for the high-frequency input/output feedthrough; a configuration that the high-frequency input/output feedthrough is fitted into the dielectric substrate and the metal frame; and a configuration that the high-frequency input/output feedthrough of the above configuration is integrated into the dielectric substrate and the dielectric frame.
In the conventional high-frequency input/output feedthrough as shown in JP-A 5-183301, it is necessary to select the length of the strip line portion forming the hermetic seal portion to be n/2 (n represents a natural number) of the signal wavelength xcex. Therefore, in a higher frequency band, for example, over 30 GHz (the millimeter wave band), it is necessary to shorten the length of the hermetic seal portion.
However, in the case where the length of the hermetic seal portion is shortened as mentioned above, there arises the following problems. Since a metal layer serving as the line portion is disposed between dielectrics which are placed above and below this portion, an adhesion strength between the dielectrics is extremely lowered and delamination is caused. In the case where such a hermetic seal portion is used in the package for housing a semiconductor element, when thermal stress is applied at the time of packaging the semiconductor element, cap-sealing, or secondarily mounting, the seal of the hermetic seal portion is impaired.
Furthermore, the thus configured high-frequency input/output feedthrough has a problem that in a high frequency band such as the millimeter wave band, due to the relationship between positions of a ground metallized layer and a seal metallized layer which form the strip line portions and a position of the strip line, or in the case where the feedthrough is used in the package for housing a semiconductor element, between positions of the metal substrate, frame and so on and a position of the strip line, resonance of a dielectric which is called slot resonance is produced, which will often show itself in a specific frequency band with the result that the transmission characteristics for high-frequency signals are extremely impaired.
Still more, in the case of adhering the plating layer to the exposed line conductor, due to a bad circulation of plating solution toward a finely structured portion, it is difficult to completely cover with the plating layer, up to a part where the microstrip line enters into the hermetic seal portion. Therefore, when moisture contained in the air adheres to the microstrip line portion in this part, the moisture contacts the metallized metal layer and the plating layer to work as electrolyte, thereby causing a battery action that a current flows between the metallized metal layer and the plating layer based on the differences in energy level of both the metals. This causes a problem that, due to so-called corrosion that the metal of the metallized metal layer having a lower energy level is gradually melt down because of the battery action, the metallized metal layer, that is, the line conductor is broken in the end.
The invention has been conducted in view of the above-discussed problems. It is an object of the invention to provide a high-frequency input/output feedthrough which transmits a high-frequency signal via a microstrip line and has a hermetic seal portion of a package, wherein the highly reliable feedthrough can prevent the hermetic seal portion from being delaminated and from being damaged due to thermal stress by improving an adhesion strength of the hermetic seal portion, has excellent transmission characteristics to a high-frequency signal in a desired specific frequency band, and causes no break in a line conductor due to corrosion.
It is another object of the invention to provide a package for housing a high-frequency semiconductor element which transmits a high-frequency signal via a microstrip line and is equipped with a high-frequency input/output feedthrough portion having a hermetic seal portion, wherein the highly reliable package can prevent the hermetic seal portion from being delaminated and from being damaged due to thermal stress by improving an adhesion strength of the hermetic seal portion, has excellent transmission characteristics to a high-frequency signal in a desired specific frequency band, and causes no break in a line conductor due to corrosion.
In a first aspect of the invention, there is provided a high-frequency input/output feedthrough comprising:
a dielectric substrate having a ground conductor on a bottom face thereof;
a wall member which is joined onto a top face of the dielectric substrate and made of a dielectric or conductive material;
a pair of line conductors formed in line with each other on both sides of the wall member on the top face of the dielectric substrate; and
an inside-layer line conductor which is formed to be in line and parallel with the pair of line conductors below the wall member inside the dielectric substrate, both ends of the inside-layer line conductor being electrically connected by through conductors to respective end portions of the pair of line conductors on both sides of the wall member, respectively,
wherein an interval of the through conductors is set to be a quarter of a wavelength of a high-frequency signal to be used.
In a second aspect of this invention, a width (W2) of the inside-layer line conductor is selected to be equal to or narrower than a width (W1) of the pair of line conductors (W1xe2x89xa7W2)
In a third aspect of this invention, the wall member is made of a dielectric material, a top face ground conductor is provided on the top face of the wall member, and side-face ground conductors are provided on respective side faces of the wall member and the dielectric substrate, respectively.
In a fourth aspect of the invention, there is provided a package for housing a high-frequency semiconductor element comprising:
a substrate having a mounting portion for mounting a high-frequency semiconductor element on a top face thereof;
a frame joined onto the substrate so as to surround the mounting portion;
an input/output feedthrough attaching portion which is formed by cutting away the frame, a bottom face of the portion being made conductive; and
a high-frequency input/output feedthrough of any one of the above-mentioned configurations which is fitted into the input/output feedthrough attaching portion.
In a fifth aspect of the invention, there is provided a package for housing a high-frequency semiconductor element comprises:
a dielectric substrate having a ground conductor on a bottom face thereof and a mounting portion for mounting a high-frequency semiconductor element on a top face thereof;
a dielectric frame joined onto the top face of the dielectric substrate so as to surround the mounting portion;
a pair of line conductors formed in line with each other on both sides of the dielectric frame on the top face of the dielectric substrate; and
an inside-layer line conductor which is formed to be in line and parallel with the pair of line conductors below the dielectric frame inside the dielectric substrate, both ends of the inside-layer line conductor being electrically connected by through conductors to respective end portions of the pair of line conductors on both sides of the dielectric frame, respectively,
wherein an interval of the through conductors is set to be a quarter of a wavelength of a high-frequency signal to be used.
In a sixth aspect of this invention, a width (W2) of the inside-layer line conductor is selected to be equal to or narrower than a width W1) of the pair of line conductors (W1xe2x89xa7W2).
According to the high-frequency input/output feedthrough of the invention, no line conductor is interposed by the dielectric substrate and the wall member, so that an adhesion strength between them is increased and hence they can be firmly joined to each other. Therefore, as a hermetic seal portion, it is possible to make the feedthrough have a highly reliable hermetic seal structure, in which delamination will not occur and the seal of the hermetic seal portion will not be impaired when thermal stress is applied at the time of packaging a semiconductor element, cap-sealing or secondarily mounting, in a case where the feedthrough is used in a package for housing a semiconductor element.
Further, regarding a high-frequency band such as the millimeter wave band, not only preferable transmission characteristics to the high-frequency signal to be used can be obtained, but also slot resonance is not generated in a specific frequency band with the result that transmission characteristics of the high-frequency signal are not degraded.
Still more, the line conductors do not have parts to enter under the wall member, and in the case of adhering the plating layer to the exposed line conductors, it is easy to completely cover the whole exposed surface of the line conductors as well as to form the thickness thereof to be uniform. Therefore, it never occurs that the metal of the base conductor layer is melt down due to corrosion, thereby breaking the line conductors.
As mentioned above, according to the invention, it is possible to improve the adhesion strength of the wall member serving as the hermetic seal portion so as to prevent the hermetic seal portion from being delaminated and being damaged due to thermal stress, as well as to provide a highly reliable high-frequency input/output feedthrough which has excellent transmission characteristics with respect to a high-frequency signal to be used in a desired specific frequency band and causes no break due to corrosion in the line conductors.
According to the high-frequency input/output feedthrough of the invention, the top face ground conductor is provided on the top face of the wall member and the side-face ground conductors are disposed on the side faces of the wall member and the dielectric substrate, respectively, whereby these ground conductors are caused to have an ideal ground potential with the result that shielding high-frequency signals is reliably attained.
Further, the package for housing a high-frequency semiconductor element of the invention is equipped with the above-described high-frequency input/output feedthrough of the invention as a high-frequency input/output feedthrough. Therefore, the package can hermetically seal in a highly reliable manner as a hermetic seal portion and can obtain preferable transmission characteristics to the high-frequency signal to be used, so that it never occurs that the metal of the base conductor layer is melt down due to corrosion to break the line conductors.
As mentioned above, according to the invention, it is possible to prevent the hermetic seal portion from being delaminated and being damaged due to thermal stress by improving the adhesion strength of the hermetic seal portion, as well as to provide a highly reliable package for housing a high-frequency semiconductor element which has excellent transmission characteristics to the high-frequency signal to be used in a desired specific frequency band, and which causes no break of the line conductor due to corrosion.